Feeders with a movable suction box, called "suction feeders", are in very widespread use in the industry for making corrugated cardboard cases and are described in many patents, such as, for example, French Nos. 1,343,103 and 1,568,091.
All these devices make use of one or more suction boxes which are movable in a longitudinal direction and the upper part of which is shut off by a horizontal plate which is provided with holes and transmits the vacuum to the sheet, and which thus makes it possible to grasp the cardboard for at least part of the extraction cycle.
These known devices are not always satisfactory, especially in the processing of sheets made of hard carboard. In fact, it is noted that the curved sheets are often laid on the suction box or boxes only partially, so that some sheets which are insufficiently flattened do not pass under the feeder blade, thus resulting in cramming which requires manual intervention by an operator.
To mitigate this type of disadvantage, it has already been suggested to use auxiliary telescopic suction cups, but such device involves a relatively high production and maintenance cost, so that a simpler and less expensive solution seems desirable.